Hawking radiation is theoretical thermal radiation predicted to be emitted by black holes due to quantum mechanical effects near the event horizon. In 1974, Stephen Hawking demonstrated that black holes, contrary to classical relativity predictions, are not completely black but instead emit particles with a thermal spectrum. This occurs because virtual particle-antiparticle pairs spontaneously form in the quantum vacuum near the event horizon; occasionally, one particle escapes while the other falls inward, resulting in a net loss of mass and energy from the black hole. The temperature is inversely proportional to the black hole's mass: T ∝ 1/M. Stellar-mass black holes (few solar masses) have enormously low Hawking temperatures (~10⁻⁸ K), making detection practically impossible given cosmic microwave background radiation (2.7 K). Conversely, primordial black holes formed in the early universe with masses ~10¹⁵ kg would have temperatures exceeding 10¹² K and would evaporate explosively through gamma-ray bursts. This paradoxically means small black holes are hotter and more unstable than massive ones—a counterintuitive result linking quantum mechanics, thermodynamics, and gravity.

The Hawking radiation framework bridges quantum field theory and general relativity by treating the black hole event horizon as a thermal boundary. The luminosity (power output) scales as L ∝ 1/M², making smaller black holes vastly more luminous. A solar-mass black hole radiates only ~10⁻²⁸ W—far dimmer than the Sun—but a 10¹⁵ kg black hole radiates ~10¹⁵ W, rivaling stellar power. The evaporation lifetime scales as t ∝ M³, so it takes the age of the universe for stellar black holes to evaporate, but primordial black holes would live only microseconds. This prediction remains unconfirmed observationally but has profound implications: it suggests black holes are not truly black, establishes thermodynamic laws in curved spacetime (black hole entropy S = k_B c³ A / (4 G ℏ)), and hints at deep connections between quantum gravity and information preservation. Modern quantum gravity theories attempt to resolve the information paradox—whether information falling into a black hole is truly lost or encoded in Hawking radiation—making this an active frontier in theoretical physics.